HelloWorld.scala defines a service that responds to HTTP requests on
GET /hello/$USERNAME with a JSON greeting. Server.scala defines
an object that extends App to start a server. sbt will find and run
any app that it finds in your project. Let’s try it:

$ sbt run

Depending on the state of your Ivy cache, several dependencies will
download. This is a good time to grab a beverage. When you come
back, you should see a line similar to this: